Ultracapacitor and method of manufacturing the same

ABSTRACT

A method for producing an ultracapacitor comprises the steps of: providing a negative porous electrode in contact with a negative conducting plate; providing a positive porous electrode in contact with a positive conducting plate; providing an ultracapacitor separator being a microporous material that separates the negative porous electrode from the positive porous electrode; providing an electrolytic solution that impregnates the negative porous electrode, the positive porous electrode, and the ultracapacitor separator; and curing the ultracapacitor at a temperature of at least 200° C.

RELATED APPLICATION

This divisional application claims the benefit of co-pending applicationSer. No. 12/021,491 filed Jan. 29, 2008 which, in turn, claimed thebenefit of earlier-filed, co-pending U.S. Provisional application No.60/886,981 filed Jan. 29, 2007.

FIELD OF INVENTION

The present application discloses an ultracapacitor with a microporousultracapacitor separator and a method for making the same.

BACKGROUND OF THE INVENTION

In general, an ultracapacitor, also known as a supercapacitor or doublelayer capacitor, is two non-reactive porous plates, or collectors,suspended within an electrolyte, with a voltage potential applied acrossthe collectors. In an individual ultracapacitor cell, the appliedpotential on the positive electrode attracts the negative ions in theelectrolyte, while the potential on the negative electrode attracts thepositive ions. A dielectric, or separator, between the two electrodesprevents the charge from moving between the two electrodes whileproviding minimal resistance to electrolyte ion flow. Currently,ultracapacitors are more expensive than batteries. Consequently, thereis a need for separators that are cost effective in order to provide anultracapacitor that has commercial viability.

In contrast with traditional capacitors, ultracapacitors do not have aconventional separator. They are based on a structure that contains aseparator that is an electrical double layer. In an electrical doublelayer, the effective thickness of the separator is exceedingly thin, andthat, combined with the very large surface area, is responsible fortheir particularly high capacitances in practical sizes. Ultracapacitorseparators are typically made of highly porous materials that provideminimal resistance to electrolyte ion movement and that at the sametime, provide electronic insulator properties between opposingelectrodes.

Various materials have been used as separators in ultracapacitors,including (1) aquagel and resorcinol formaldehyde polymer, (2)polyolefin film, (3) nonwoven polystyrene cloth (4) acrylic resin fibersand (5) nonwoven polyester film. Other materials such as porouspolyvinyl chloride, porous polycarbonate membrane and fiberglass paperare suitable as separators for ultracapacitors. Some separator materialssuch as polyesters, show high ionic resistance in nonaqueous electrolytebecause of poor wettability by organic solvents such as propylenecarbonates. On the other hand, some of the separator materialsdemonstrate good features as separators in nonaqueous electrolyte butare too expensive for commercialization.

One problem associated with today's ultracapacitors is they are verysensitive to the electrical resistance of the ultracapacitor cell. Theinternal electrical resistance of the ultracapacitor cell impacts theperformance or energy output. The lower the electrical resistance of theultracapacitor separator, the better the performance of the cell. Forexample, large packs (modules) of multiple ultracapacitors which areneeded in Hybrid Vehicles create internal heat during operations.Location of the module near heat sources such as the engine or insidethe cabin exposes the ultracapacitors to high heats. The heat generatedduring operation along with the outside environmental temperature cancreate a high heat environment which, in turn, exposes theultracapacitor separator to high heats. High heat increases theelectrical resistance of most of the ultracapacitor separators usedtoday. Thus, it is desired to have a robust ultracapacitor separatorwhich can withstand these high temperatures during the life of theultracapacitor and maintain both the physical and electrical propertiesof the separator material for the life of the ultracapacitor.

Another problem associated with ultracapacitor cells is moisture.Moisture inside the high surface area carbon electrodes of aultracapacitor degrades the performance during life by increasing theinternal resistance of the cell. Therefore, one must attempt to removethe moisture in order to have an effective ultracapacitor. To drive offthe moisture inside the ultracapacitor cell, high temperature curing isrequired. This process includes heating the ultracapacitor to a hightemperature so that the moisture will dry out. This curing process is afunction of temperature and time where the higher the curing temperaturethe less time required to adequately cure the ultracapacitor. Typicalultracapacitor separators begin to increase in electrical resistance incuring temperature above 150° C. for 12 hours. Thus, an ultracapacitorseparator which can withstand higher curing temperatures up to 200° C.and maintain its initial properties will allow for higher performancecells as more moisture can be removed. Therefore, in order to save moneyand speed up the production of an ultracapacitor, there is a need for anultracapacitor separator material that can be heated to a highertemperature while still substantially maintaining its resistanceproperties.

The instant invention utilizes a microporous membrane as anultracapacitor separator. A microporous membrane comprising a very highmolecular weight polyolefin and an inert filler material was taught byLarsen, U.S. Pat. No. 3,351,495. The general principles and proceduresof U.S. Pat. No. 3,351,495 are incorporated herein by reference. Kono etal., U.S. Pat. No. 4,600,633 teaches a polyethylene superthin film and aprocess for the production of the same. In this process an ultra highmolecular weight polyethylene (herein after UHMWPE) is dissolved in asolvent then extruded to form a gel sheet. The gel sheet then undergoesa first extraction step to remove the solvent. After the firstextraction, the sheet is heated and stretched. The stretched sheet thenundergoes a second extraction step to remove solvent. The resultingproduct then undergoes a compression treatment at a temperature of 80°to 140° centigrade. This reference does not use a filler in its UHMWPE.The gel sheet is not calendered prior to solvent extraction. Theresulting product is a thin film with a tensile modulus of at least 2000kg/cm² a breaking strength of at least 500 kg/cm² and which, issubstantially free from pores. In addition, U.S. patent application Ser.No. 11/006,333 to Miller et. al. discloses a microporous materialsimilar to the material used herein, however, this material is notdirected for use as an ultracapacitor separator.

The instant invention of an ultracapacitor with a microporousultracapacitor separator and a method making the same is designed toaddress the aforementioned problems.

SUMMARY OF THE INVENTION

The instant invention is directed toward a method for producing anultracapacitor. The method comprises the steps of: providing a negativeporous electrode in contact with a negative conducting plate; providinga positive porous electrode in contact with a positive conducting plate;providing an ultracapacitor separator being a microporous material thatseparates the negative porous electrode from the positive porouselectrode; providing an electrolytic solution; and curing theultracapacitor at a temperature of at least 200° C. The microporousmaterial includes: an ultrahigh molecular weight polyethylene (UHMWPE)and a particulate filler distributed throughout the microporousmaterial. The filler constitutes from about 5 percent to 95 percent byweight of the microporous material. The microporous material has anetwork of interconnecting pores communicating throughout themicroporous material. The pores constitute at least 25 percent by volumeof the microporous material. These pores create a pore distributionwhere the microporous material has no pores greater in size than 1.0micrometers and the change in volume divided by log d for the pores ofthis microporous material is less than 2 cc/g for the entire poredistribution. The electrolytic solution impregnates the negative porouselectrode, the positive porous electrode, and the ultracapacitorseparator.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings information about some of the embodiments of the invention; itbeing understood, however, that this invention is not limited to theprecise information shown.

FIG. 1 is a front sectional view of one embodiment of an ultracapacitorutilizing the microporous ultracapacitor separator material of theinstant invention;

FIG. 2 is a graph of data obtained using a test called compressionthermomechanical analysis (compression TMA) which measures the thicknessof an ultracapacitor separator according to the instant invention as afunction of temperature to show the amount the material shrinks, melts,deforms when the material is heated to 500° C.;

FIG. 3 is a graph of data which shows the electrical resistancemeasurements as a function of temperature for both an ultracapacitorseparator of the instant invention and a sample of paper which ispresently used in ultracapacitor applications to show how theultracapacitor separator has a lower resistance when heated at aconstant heating rate (60° C./min);

FIG. 4 is a graph of data obtained using a mercury Porosimeter whichplots pore diameter to pore volume for an ultracapacitor separator madeaccording to the instant invention, where post stretch calendering isperformed at moderate pressure;

FIG. 5 is a graph of data obtained using a mercury Porosimeter whichplots pore diameter to pore volume for an ultracapacitor separator madeaccording to the instant invention, where post stretch calendering isperformed at a higher compression pressure.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, wherein like numerals indicate like elements,there is shown in FIG. 1 one embodiment of an ultracapacitor 10 madeaccording to the method of manufacturing an ultracapacitor according tothe instant invention. Ultracapacitor 10 may be any type or size ofultracapacitor. Ultracapacitor 10 may be used alone or in series withone or more other ultracapacitors.

As shown in FIG. 1, ultracapacitor 10 may include a negative porouselectrode 12 and a positive porous electrode 16. Negative porouselectrode 12 may be in contact with a negative conducting plate 14.Positive porous electrode 16 may be in contact with a positiveconducting plate 14. Ultracapacitor separator 20 may separate negativeporous electrode 13 from positive porous electrode 16. Negative porouselectrode 12, positive porous electrode 16, and ultracapacitor separator20 may be impregnated by an electrolytic solution 22.

A method for producing ultracapacitor 10 may comprise the followingsteps: providing negative porous electrode 12 in contact with negativeconducting plate 14; providing positive porous electrode 16 in contactwith positive conducting plate 18; providing ultracapacitor separator 20being a microporous material separating negative porous electrode 12from positive porous electrode 16; providing electrolytic solution 22where electrolytic solution 22 may impregnate negative porous electrode12, positive porous electrode 16, and ultracapacitor separator 20; andcuring ultracapacitor 10 at a temperature of at least 200° C.

Ultracapacitor separator 20 may be included in ultracapacitor 10.Ultracapacitor separator 20 may be for separating negative porouselectrode 12 from positive porous electrode 16. Ultracapacitor separator20 may provide minimal resistance to electrolyte ion movement betweenelectrolytic solution 22. Ultracapacitor separator 20 may also providemaximum electronic insulator properties between negative porouselectrode 12 and positive porous electrode 16. Ultracapacitor separator20 may have a change in thickness of less than 8% at a curingtemperature of at least 200° C. (see FIG. 2). Ultracapacitor separator20 may also have a surface resistance of less than 30 ohms/cm² at anytemperature less than 200° C. (see FIG. 3).

In FIG. 2, a microporous material for ultracapacitor separator 20 wasmade according to the instant invention and tested using a test calledcompression thermomechanical analysis (compression TMA). The testinvolves measuring the thickness of a film sample as a function oftemperature. During the experiment, the temperature is increased at aconstant heating rate from room temperature until the final desiredtemperature is reached. In this case, the heating rate which was usedwas 10° C./min. As shown in FIG. 2, the microporous material shrinks asmall amount, less than 8%, at a temperature of at least 200° C. Thus,the microporous material used for ultracapacitor separator 10 can beexposed to high temperatures without substantially deforming, shrinkingor melting. These properties of the microporous material shown in FIG. 2allows for ultracapacitor 10 to be exposed to the step of curing theultracapacitor 10 at a temperature of at least 200° C., while stillsubstantially maintaining its separator properties, i.e., resistance.

In FIG. 3, a commonly known paper ultracapacitor separator and threemicroporous materials for ultracapacitor separator 20 were madeaccording to the instant invention and were tested for electricalresistance measurements as a function of temperature. The data wasgenerated from the beginning temperature of the experiment to the finaltemperature using a constant heating rate. In this case, the heatingrate which was used was 60 C/min. This test shows the lower resistanceof these three microporous materials at temperatures from 20° C. to 200°C. compared to a commonly used paper separator. According to the resultsshown in FIG. 3, an ultracapacitor made according to the instantinvention will have lower resistance than the prior art, which mayresult in better performance of ultracapacitor 10.

Ultracapacitor 20 may be made of a microporous material that comprisesan ultrahigh molecular weight polyethylene (UHMWPE) and a particulatefiller distributed throughout the microporous material. The filler mayconstitute from about 5 percent to 95 percent by weight of themicroporous material. The microporous material may have a network ofinterconnecting pores communicating throughout the microporous material,and the pores may constitute at least 25 percent by volume of themicroporous material. These pores may create a pore distribution wherethe microporous material has no pores greater in size than 1.0micrometers and the change in volume divided by log d for the pores ofthis microporous material is less than 2 cc/g for the entire poredistribution.

A method of making the microporous material of ultracapacitor separator20 may include the following steps: providing an ultrahigh molecularweight polyethylene (herein after UHMWPE); providing a particulatefiller; and providing a processing plasticizer where the processingplasticizer is a liquid at room temperature. The UHMWPE, filler andplasticizer are all described in greater detail below. The UHMWPE,filler and plasticizer are mixed together to form a mixture. The mixtureis extruded through a die (e.g. slot die or blown film die) to form asheet. The sheet may be further processed, by casting onto a chilledroller, or calendered, or blown. The cast or calendered sheet is thensubjected to an extraction step to partially (or fully) remove theplasticizer and forms thereby a microporous matrix. The matrix comprisesUHMWPE, plasticizer if not fully extracted, and the particulate fillerdistributed throughout the matrix. The filler constitutes from 5 percentto 95 percent by weight of the microporous matrix. The microporousmatrix has a network of interconnecting pores communicating throughoutthe microporous matrix. The pores constitute from 25 percent to 90percent by volume of the microporous matrix. The microporous matrix isstretched. The stretching process is described in greater detail below.The stretched microporous matrix is not dimensionally stable at elevatedtemperatures. The stretched microporous matrix is subsequentlycalendared to produce the final microporous material that isdimensionally stable even at elevated temperatures.

Ultrahigh molecular weight polyethylene (UHMWPE) can be defined as apolyethylene having an intrinsic viscosity of least about 18deciliters/gram. In many cases the intrinsic viscosity is at least about19 deciliters/gram. Although there is no particular restriction on theupper limit of the intrinsic viscosity, the intrinsic viscosity isfrequently in the range of from about 18 to about 39 deciliters/gram. Anintrinsic viscosity in the range of from about 18 to about 32deciliters/gram is most common.

As used herein and in the claims, intrinsic viscosity is determined byextrapolating to zero concentration the reduced viscosities or theinherent viscosities of several dilute solutions of the UHMWPE where thesolvent is freshly distilled decahydronaphthalene to which 0.2 percentby weight, 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid,neopentanetetrayl ester [CAS Registry No. 6683-19-8] has been added. Thereduced viscosities or the intrinsic viscosities of the UHMWPE areascertained from relative viscosities obtained at 135° C. using anUbbelohde No. 1 viscometer in accordance with the general procedures ofASTM D 4020-81, except that several dilute solutions of differingconcentration are employed. ASTM D 4020-81 is, in its entirety,incorporated herein by reference.

Sufficient UHMWPE should be present in the matrix to provide itsproperties to the microporous material for an ultracapacitor separator.Other thermoplastic organic polymers may also be present in the matrix,so long as their presence does not materially affect the properties ofthe microporous material for an ultracapacitor separator in an adversemanner. The amount of the other thermoplastic polymers which may bepresent depends upon the nature of such polymers. In general, a greateramount of other thermoplastic organic polymer may be used if themolecular structure contains little branching, few long sidechains, andfew bulky side groups, than when there is a large amount of branching,many long sidechains, or many bulky side groups. For this reason, theexemplary thermoplastic organic polymers that may be mixed with theUHMWPE are low density polyethylene, high density polyethylene,poly(tetrafluoroethylene), polypropylene, copolymers of ethylene, suchas ethylene-butene or ethylene-hexene, copolymers of propylene,copolymers of ethylene and acrylic acid, and copolymers of ethylene andmethacrylic acid. If desired, all or a portion of the carboxyl groups ofcarboxyl-containing copolymers may be neutralized with sodium, zinc orthe like. Usually at least about 70 percent UHMWPE (or 70 percent UHMWPEand other thermoplastic organic polymers), based on the weight of thematrix, will provide the desired properties to the microporous materialfor a capacitor separator.

The particulate filler may be in the form of ultimate particles,aggregates of ultimate particles, or a combination of both. In mostcases, at least about 90 percent by weight of the filler has grossparticle sizes in the range of from about 5 to about 40 micrometers. Ifthe filler used is titanium dioxide (TiO2) the gross particle size canrange from 0.005 to 45 micrometers. In another embodiment using titaniumdioxide (TiO2) as a filler, the gross particle size ranges from 0.1 to 5micrometers. In another case, at least about 90 percent by weight of thefiller has a gross particle size in the range of from about 10 to about30 micrometers. It is expected that filler agglomerates will be reducedin size during processing of the ingredients. Accordingly, thedistribution of gross particle sizes in the microporous material for acapacitor separator may be smaller than in the raw filler itself.Particle size is determined by use of a Model TAII Coulter counter(Coulter Electronics, Inc.) according to ASTM C 690-80, but modified bystirring the filler for 10 minutes in Isoton II electrolyte (CurtinMatheson Scientific, Inc.) using a four-blade, 4.445 centimeter diameterpropeller stirrer. ASTM C 690-80 is, in its entirety, incorporatedherein by reference.

The particulate filler will on average have an ultimate particle size(irrespective of whether or not the ultimate particles are agglomerated)which is less than about 30 micrometer as determined by transmissionelectron microscopy. Often the average ultimate particle size is lessthan about 0.05 micrometer. In one embodiment the average ultimateparticle size of filler is approximately 20 micrometers (when aprecipitated silica is used).

Use of fillers in a polymer matrix is well documented. In generalexamples of suitable fillers include siliceous fillers, such as: silica,mica, montmorillonite, kaolinite, asbestos, talc, diatomaceous earth,vermiculite, natural and synthetic zeolites, cement, calcium silicate,clay, aluminum silicate, sodium aluminum silicate, aluminumpolysilicate, alumina silica gels, and glass particles. In addition tothe siliceous fillers other particulate substantially water-insolublefillers may also be employed. Examples of such optional fillers includecarbon black, activated carbon, carbon fibers, charcoal, graphite,titanium oxide, iron oxide, copper oxide, zinc oxide, lead oxide,tungsten, antimony oxide, zirconia, magnesia, alumina, molybdenumdisulfide, zinc sulfide, barium sulfate, strontium sulfate, calciumcarbonate, and magnesium carbonate.

Silica and the clays are the most useful siliceous fillers. Of thesilicas, precipitated silica, silica gel, or fumed silica is most oftenused.

The particulate filler which has been found to work well is precipitatedsilica. It is important to distinguish precipitated silica from silicagel, inasmuch as these different materials have different properties.Reference in this regard is made to R. K. Iler, The Chemistry of Silica,John Wiley & Sons, New York (1979), Library of Congress Catalog No. QD181.S6144, the entire disclosure of which is incorporated herein byreference. Note especially pages 15-29, 172-176, 218-233, 364-365,462-465, 554-564, and 578-579. Silica gel is usually producedcommercially at low pH by acidifying an aqueous solution of a solublemetal silicate, typically sodium silicate, with acid. The acid employedis generally a strong mineral acid such as sulfuric acid or hydrochloricacid although carbon dioxide is sometimes used. Inasmuch as there isessentially no difference in density between gel phase and thesurrounding liquid phase while the viscosity is low, the gel phase doesnot settle out, that is to say, it does not precipitate. Silica gel,then, may be described as a non-precipitated, coherent, rigid,three-dimensional network of contiguous particles of colloidal amorphoussilica. The state of subdivision ranges from large, solid masses tosubmicroscopic particles, and the degree of hydration from almostanhydrous silica to soft gelatinous masses containing on the order of100 parts of water per part of silica by weight, although the highlyhydrated forms are only rarely used in the present invention.

Precipitated silica on the other hand, is usually produced commerciallyby combining an aqueous solution of a soluble metal silicate, ordinarilyalkali metal silicate such as sodium silicate, and an acid so thatcolloidal particles will grow in weakly alkaline solution and becoagulated by the alkali metal ions of the resulting soluble alkalimetal salt. Various acids may be used, including the mineral acids, butthe preferred material is carbon dioxide. In the absence of a coagulant,silica is not precipitated from solution at any pH. The coagulant usedto effect precipitation may be the soluble alkali metal salt producedduring formation of the colloidal silica particles, it may be addedelectrolyte such as a soluble inorganic or organic salt, or it may be acombination of both. Precipitated silica, then, may be described asprecipitated aggregates of ultimate particles of colloidal amorphoussilica that have not at any point existed as macroscopic gel during thepreparation. The sizes of the aggregates and the degree of hydration mayvary widely.

Precipitated silica powders differ from silica gels in that they havebeen pulverized in ordinarily having a more open structure, that is, ahigher specific pore volume. However, the specific surface area ofprecipitated silica as measured by the Brunauer, Emmett, Teller (BET)method using nitrogen as the adsorbate, is often lower than that ofsilica gel.

Many different precipitated silicas may be employed in the presentinvention. Precipitated silicas are those obtained by precipitation froman aqueous solution of sodium silicate using a suitable acid such assulfuric acid or hydrochloric acid. Carbon dioxide can also be used toprecipitate the silica. Such precipitated silicas are known andprocesses for producing them are described in detail in U.S. Pat. No.2,940,830, the entire disclosure of which is incorporated herein byreference, including the processes for making precipitated silicas andthe properties of the products.

In the proceeding process for producing a microporous matrix, extrusionand calendering are facilitated when the substantially water-insolublefiller carries much of the processing plasticizer. The capacity of thefiller particles to absorb and hold the processing plasticizer is afunction of the surface area of the filler. It is therefore preferredthat the filler have a high surface area. High surface area fillers arematerials of very small particle size, materials having a high degree ofporosity or materials exhibiting both characteristics. Usually thesurface area of the filler itself is in the range of from about 20 toabout 400 square meters per gram as determined by the Brunauer, Emmett,Teller (BET) method according to ASTM C 819-77 using nitrogen as theadsorbate but modified by outgassing the system and the sample for onehour at 130° C. Preferably the surface area is in the range of fromabout 25 to about 350 square meters per gram. ASTM C 819-77 is, in itsentirety, incorporated herein by reference. Inasmuch as it is desirableto essentially retain the filler in the microporous matrix sheet, it ispreferred that the substantially water-insoluble filler be substantiallyinsoluble in the processing plasticizer and substantially insoluble inthe organic extraction liquid when microporous matrix sheet is producedby the above process.

The processing plasticizer is typically a liquid at room temperature andusually it is processing oil such as paraffinic oil, naphthenic oil, oran aromatic oil. Suitable processing oils include those meeting therequirements of ASTM D 2226-82, Types 103 and 104. It has been foundthat oils which have a pour point of less than 22° C. according to ASTMD 97-66 (reapproved 1978) work well. Oils having a pour point of lessthan 10° C. also work well. Examples of suitable oils include, but arenot limited to, Shellflex® 412 and Shellflex® 371 oil (Shell Oil Co.)which are solvent refined and hydrotreated oils derived from naphtheniccrude. ASTM D 2226-82 and ASTM D 97-66 (reapproved 1978) are, in theentireties, incorporated herein by reference. It is expected that othermaterials, including the phthalate ester plasticizers such as dibutylphthalate, bis (2-ethylhexyl)phthalate, diisodecyl phthalate,dicyclohexyl phthalate, butyl benzyl phthalate, ditridecyl phthalate andwaxes, will function satisfactorily as processing plasticizers. Theprocessing plasticizer has little solvating effect on the thermoplasticorganic polymer at 60° C., only a moderate solvating effect at elevatedtemperatures on the order of about 100° C., and a significant solvatingeffect at elevated temperatures on the order of about 200° C.

Minor amounts, usually less than about 5 percent by weight, of othermaterials used in processing such as lubricant, organic extractionliquid, surfactant, water, and the like, may optionally also be present.Yet other materials introduced for particular purposes may optionally bepresent in the microporous material in small amounts, usually less thanabout 15 percent by weight. Examples of such materials includeantioxidants, ultraviolet light absorbers, flame retardants, reinforcingfibers such as carbon fiber or chopped glass fiber strand, dyes,pigments, and the like. The balance of the microporous material,exclusive of filler and any impregnate applied for one or more specialpurposes, is essentially the thermoplastic organic polymer andplasticizer (if not fully extracted).

Then the filler, thermoplastic organic polymer powder, processingplasticizer and other additives are mixed until a substantially uniformmixture is obtained. This uniform mixture may also contain otheradditives such as minor amounts of lubricant and antioxidant. The weightratio of filler to polymer powder employed in forming the mixture isessentially the same as that of the stretched microporous material to beproduced. The ratio of filler to UHMWPE in this mixture is in the rangeof from about 1:9 to about 15:1 filler to UHMWPE by weight. Theparticulate filler constitutes from about 5 percent to about 95 percentby weight of that microporous material. Frequently, such fillerconstitutes from about 45 percent to about 90 percent by weight of themicroporous material. From about 55 percent to about 80 percent byweight is used in one of the embodiments of the invention. The ratio ofthe UHMWPE to the processing plasticizer is 1:30 to 3:2 by weight. Ratioof filler to processing plasticizer is 1:15 to 3:1 by weight.

In the extrusion and calendering process, the mixture, together withadditional processing plasticizer, is introduced to the heated barrel ofa screw extruder. Attached to the extruder is a sheeting die. Acontinuous sheet formed by the die is forwarded without drawing to apair of heated calender rolls acting cooperatively to form continuoussheet of lesser thickness than the continuous sheet exiting from thedie.

The continuous sheet is subjected to an extraction step where processingplasticizer is partially or fully removed there from. The extractionstep may include one or more steps. For example, the continuous sheetfrom the calender then passes to a first extraction zone where theprocessing plasticizer is substantially removed by extraction with anorganic liquid which is a good solvent for the processing plasticizer, apoor solvent for the organic polymer, and more volatile than theprocessing plasticizer. Usually, but not necessarily, both theprocessing plasticizer and the organic extraction liquid aresubstantially immiscible with water. There are many organic extractionliquids that can be used. Examples of suitable organic extractionliquids include but are not limited to hexane, alkanes of varying chainlengths, 1,1,2-trichloroethylene, perchloroethylene, 1,2-dichloroethane,1,1,1-trichloroethane, 1,1,2-trichloroethane, methylene chloride,chloroform, isopropyl alcohol, diethyl ether and acetone. The continuoussheet then passes to a second extraction zone where the residual organicextraction liquid is substantially removed by: heat, steam and/or water.The continuous sheet is then passed through a forced air dryer forsubstantial removal of residual water and remaining residual organicextraction liquid. From the dryer the continuous sheet, which is amicroporous matrix, is passed to a take-up roll.

The microporous matrix comprises a filler, UHMWPE, and optionalmaterials in essentially the same weight proportions as those discussedabove in respect of the stretched microporous matrix. The matrix mightalso have some plasticizer if it is not fully extracted. The residualprocessing plasticizer content is usually less than 20 percent by weightof the microporous matrix and this may be reduced even further byadditional extractions using the same or a different organic extractionliquid.

In the microporous matrix, the pores constitute from about 25 to about90 percent by volume. In many cases, the pores constitute from about 30to about 80 percent by volume of the microporous matrix. One of theembodiments has from 50 to 75 percent of the volume of the microporousmatrix is pores. The porosity of the microporous matrix, expressed aspercent by volume. Unless impregnated, the porosity of the stretchedmicroporous matrix is greater than the porosity of the microporousmatrix before stretching.

As used herein and in the claims, the porosity (also known as voidvolume) of the microporous material, expressed as percent by volume, isdetermined according to the equation:

Porosity=100[1−d ₁ /d ₂]

where d₁ is the density of the sample which is determined from thesample weight and the sample volume as ascertained from measurements ofthe sample dimensions and d₂ is the density of the solid portion of thesample which is determined from the sample weight and the volume of thesolid portion of the sample. The volume of the solid portion of thesample can be determined using a Quantachrome stereopycnometer(Quantachrome Corp.) in accordance with the accompanying operatingmanual.

The volume average diameter of the pores of the microporous sheet can bedetermined by mercury porosimetry using an Autoscan mercury porosimeter(Quantachrome Corp.). Mercury Intrusion/Extrusion is based on forcingmercury (a non-wetting liquid) into a porous structure under tightlycontrolled pressures. Since mercury does not wet most substances andwill not spontaneously penetrate pores by capillary action, it must beforced into the voids of the sample by applying external pressure. Thepressure required to fill the voids is inversely proportional to thesize of the pores. Only a small amount of force or pressure is requiredto fill large voids, whereas much greater pressure is required to fillvoids of very small pores.

In operating the porosimeter, a scan is made in the high pressure range(from about 138 kilopascals absolute to about 227 megapascals absolute).If about 2 percent or less of the total intruded volume occurs at thelow end (from about 138 to about 250 kilopascals absolute) of the highpressure range, the volume average pore diameter is taken as twice thevolume average pore radius determined by the porosimeter. Otherwise, anadditional scan is made in the low pressure range (from about 7 to about165 kilopascals absolute) and the volume average pore diameter iscalculated according to the equation:

$d = {{2\left\lbrack {\frac{v_{1}r_{1}}{w_{1}} + \frac{v_{2}r_{2}}{w_{2}}} \right\rbrack}/\left\lbrack {\frac{v_{1}}{w_{1}} + \frac{v_{2}}{w_{2}}} \right\rbrack}$

where d is the volume average pore diameter, v₁ is the total volume ofmercury intruded in the high pressure range, v₂ is the total volume ofmercury intruded in the low pressure range, r₁ is the volume averagepore radius determined from the high pressure scan, r₂ is the volumeaverage pore radius determined from the low pressure scan, w₁ is theweight of the sample subjected to the high pressure scan, and w₂ is theweight of the sample subjected to the low pressure scan.

Large pores require lower pressures for the mercury to intrude into thepore volume while smaller pores require the higher pressures forintrusion into the pore volumes. In most microporous material,approximately 20% of the pores are smaller than 0.02 micrometers.DV/logd represents the change in pore volume with the change in log ofpore diameter. Thus in most microporous materials there a large numberof pores that have a diameter of approximately 0.016 micrometers, andthe peak height is several magnitudes higher than any other peak. Inthese material, the peak areas and heights represent the relative numberof pores at the corresponding log of pore diameter.

The volume average diameter of the pores of the common microporousmatrix is usually a distribution from about 0.01 to about 1.0micrometers. By stretching the precursor material one can obtain poreswhich are greater than 1 micrometer in size. Depending on the amount ofstretch it is possible to obtain pores greater than 20 to 30micrometers. Then through the subsequent calendering step the pore sizecan be selectively reduced from the enlarged pore distribution. Oneexample at this modified distribution of the average diameter of thepores is in the range of from about 0.01 to about 0.8 micrometers forthe resulting microporous material which is stretched and calendered. Inanother embodiment the resulting microporous material has a distributionof average diameter of the pores of from about 0.01 to about 0.6micrometers, as seen in FIG. 4. The volume average diameter of the poresof the microporous matrix is determined by the mercury porosimetrymethod.

The stretched microporous matrix may be produced by stretching themicroporous matrix in at least one stretching direction to a stretchratio of at least about 1.5. In many cases, the stretch ratio is atleast about 1.7. In another embodiment it is at least about 2.Frequently, the stretch ratio is in the range of from about 1.5 to about15. Often the stretch ratio is in the range of from about 1.7 to about10. In another embodiment, the stretch ratio is in the range of fromabout 2 to about 6. As used herein and in the claims, the stretch ratiois determined by the formula:

S=L ₂ /L ₁

where S is the stretch ratio, L₁ is the distance between two referencepoints located on the microporous matrix and on a line parallel to thestretching direction, and L₂ is the distance between the same tworeference points located on the stretched microporous material. When thestretching is done in two directions, the stretching in the twodirections may be performed either sequentially or simultaneously.

The temperatures at which stretching is accomplished may vary widely.Stretching may be accomplished at about ambient room temperature, butusually elevated temperatures are employed. The microporous matrix maybe heated by any of a wide variety of techniques prior to, during,and/or after stretching. Examples of these techniques include radiativeheating such as that provided by electrically heated or gas firedinfrared heaters, convective heating such as that provided byrecirculating hot air, and conductive heating such as that provided bycontact with heated rolls. The temperatures which are measured fortemperature control purposes may vary according to the apparatus usedand personal preference. For example, temperature-measuring devices maybe placed to ascertain the temperatures of the surfaces of infraredheaters, the interiors of infrared heaters, the air temperatures ofpoints between the infrared heaters and the microporous matrix, thetemperatures of circulating hot air at points within the apparatus, thetemperature of hot air entering or leaving the apparatus, thetemperatures of the surfaces of rolls used in the stretching process,the temperature of heat transfer fluid entering or leaving such rolls,or film surface temperatures. In general, the temperature ortemperatures are controlled such that the microporous matrix isstretched about evenly so that the variations, if any, in film thicknessof the stretched microporous matrix are within acceptable limits and sothat the amount of stretched microporous matrix outside of those limitsis acceptably low. It will be apparent that the temperatures used forcontrol purposes may or may not be close to those of the microporousmatrix itself since they depend upon the nature of the apparatus used,the locations of the temperature-measuring devices, and the identitiesof the substances or objects whose temperatures are being measured.

In view of the locations of the heating devices and the line speedsusually employed during stretching, gradients of varying temperaturesmay or may not be present through the thickness of the microporousmatrix. Also because of such line speeds, it is impracticable to measurethese temperature gradients. The presence of gradients of varyingtemperatures, when they occur, makes it unreasonable to refer to asingular film temperature. Accordingly, film surface temperatures, whichcan be measured, are best used for characterizing the thermal conditionof the microporous matrix. These are ordinarily about the same acrossthe width of the microporous matrix during stretching although they maybe intentionally varied, as for example, to compensate for microporousmatrix having a wedge-shaped cross-section across the sheet. Filmsurface temperatures along the length of the sheet may be about the sameor they may be different during stretching.

The film surface temperature at which stretching is accomplished mayvary widely, but in general they are such that the microporous matrix isstretched about evenly, as explained above. In most cases, the filmsurface temperatures during stretching are in the range of from about20° C. to about 220° C. Often such temperatures are in the range of fromabout 50° C. to about 200° C. From about 75° C. to about 180° C. isanother range in this embodiment.

Stretching may be accomplished in a single step or a plurality of stepsas desired. For example, when the microporous matrix is to be stretchedin a single direction (uniaxial stretching), the stretching may beaccomplished by a single stretching step or a sequence of stretchingsteps until the desired final stretch ratio is attained. Similarly, whenthe microporous matrix is to be stretched in two directions (biaxialstretching), the stretching can be conducted by a single biaxialstretching step or a sequence of biaxial stretching steps until thedesired final stretch ratios are attained. Biaxial stretching may alsobe accomplished by a sequence of one or more uniaxial stretching stepsin one direction and one or more uniaxial stretching steps in anotherdirection. Biaxial stretching steps where the microporous matrix isstretched simultaneously in two directions and uniaxial stretching stepsmay be conducted in sequence in any order. Stretching in more than twodirections is within contemplation. It may be seen that the variouspermutations of steps are quite numerous. Other steps, such as cooling,heating, sintering, annealing, reeling, unreeling, and the like, mayoptionally be included in the overall process as desired.

Various types of stretching apparatus are well known and may be used toaccomplish stretching of the microporous matrix according to the presentinvention. Uniaxial stretching is usually accomplished by stretchingbetween two rollers wherein the second or downstream roller rotates at agreater peripheral speed than the first or upstream roller. Uniaxialstretching can also be accomplished on a standard tentering machine.Biaxial stretching may be accomplished by simultaneously stretching intwo different directions on a tentering machine. More commonly, however,biaxial stretching is accomplished by first uniaxially stretchingbetween two differentially rotating rollers as described above, followedby either uniaxially stretching in a different direction using a tentermachine or by biaxially stretching using a tenter machine. The mostcommon type of biaxial stretching is where the two stretching directionsare approximately at right angles to each other. In most cases wherecontinuous sheet is being stretched, one stretching direction is atleast approximately parallel to the long axis of the sheet (machinedirection) and the other stretching direction is at least approximatelyperpendicular to the machine direction and is in the plane of the sheet(transverse direction).

After the microporous matrix has been stretched either uniaxially orbiaxially then the stretched microporous matrix is again calendered. Thestretched microporous matrix is forwarded to a pair of heated calenderrolls acting cooperatively to form a membrane of lesser thickness thanthe microporous matrix exiting from the stretching apparatus. Byregulating the pressure exerted by these calender rolls along with thetemperature, the pore size of the final membrane can be controlled asdesired. This allows the manufacturer to adjust the average pore sizewith a degree of control which heretofore has not been seen. The finalpore size will affect other properties such as the Gurley value of themembrane, as well as, improving the dimensional stability of themembrane at temperatures above room temperature of 20° to 25°centigrade.

FIGS. 4-5 provide plots of data collected from mercury porosimetry. FIG.4 is a graph showing pore diameter in micrometers for a membranebiaxially stretched and subsequently calendered through a gap of 25micrometers. FIG. 5 is a graph showing pore diameter in micrometers fora membrane biaxially stretched and subsequently calendered at a highcompression pressure through a minimal gap. FIGS. 4-5 show thatcompression substantially changes the pore size distribution which ispresent in the material. Also, it is possible to adjust the pore sizedistribution by adjusting the compression conditions.

The final membrane is the result of stretching a precursor material andsubsequently compressing it to have at least a 5% reduction in thicknessof the stretched precursor material, which is defined above as themicroporous matrix. This microporous material consists essentially of(or comprises): an ultrahigh molecular weight polyethylene (UHMWPE) anda particulate filler distributed throughout the microporous material,where the filler constitutes from about 5 percent to 95 percent byweight of the microporous material. The microporous material has anetwork of interconnecting pores communicating throughout themicroporous material, the pores constituting at least 25 percent byvolume of the microporous material. The microporous material has atensile strength in the machine direction (MD) of greater than 20 N/mm²;the microporous material also has a wet out time of less than 180seconds when silica is used as the filler. It has been observed thatthis microporous material has an electrical resistance of less than 130mohm/mm².

An ultracapacitor separator may comprise a microporous material wherethe microporous material consists essentially of: (or comprises) anultrahigh molecular weight polyethylene (UHMWPE) and a particulatefiller distributed throughout the microporous material, where the fillerconstitutes from about 5 percent to 95 percent by weight of themicroporous material. The microporous material has a network ofinterconnecting pores communicating throughout the microporous material,with the pores constituting at least 25 percent by volume of themicroporous material. This microporous material has no pores greater insize than 1.0 micrometers; and where change in volume divided by log dfor the pores of this microporous material is less than 2 cc/g.

The resulting microporous material which has been both stretched andcalendered exhibits shrink in the machine direction of less than 10% andhas tensile strength of greater than 25 N/mm² in the machine direction(MD).

The microporous material described above can also include a secondpolymer. The UHMWPE is mixed with a high density (HD) polyethylene toproduce a polyolefin mixture, where the polyolefin mixture has at least50% UHMWPE by weight. The filler used with this polyolefin mixture is ina range of from about 1:9 to about 15:1 filler to polyolefin mixture byweight. The resulting matrix consists essentially of (or comprises)UHMWPE and HD polyethylene and the particulate filler distributedthroughout the matrix. This microporous material has a machine direction(MD) tensile strength of greater than 25 N/mm².

With higher compression after the stretch the resulting microporousmaterial consists essentially of: (or comprises) an ultrahigh molecularweight polyethylene (UHMWPE) and a particulate filler distributedthroughout the microporous material, where the filler constitutes fromabout 5 percent to 95 percent by weight of the microporous material. Themicroporous material has a network of interconnecting porescommunicating throughout the microporous material, with the poresconstituting at least 25 percent by volume of the microporous material.Since the compression pressure determines the resulting pore sizedistribution, the pore structure is highly adjustable. For instance,this microporous material in FIG. 4 has no pores greater in size than0.50 micrometers. The median pore size is between or equal to 0.01 and0.3 micrometers and the pores vary in size by plus or minus 0.2micrometers.

The resulting microporous material which has been both stretched andcalendered exhibits shrink in the machine direction of less than 10% andhas tensile strength of greater than 25 N/mm² in the machine direction(MD).

The microporous material described above can also include a secondpolymer. The UHMWPE is mixed with a high density (HD) polyethylene toproduce a polyolefin mixture, where the polyolefin mixture has at least50% UHMWPE by weight. The filler used with this polyolefin mixture is ina range of from about 1:9 to about 15:1 filler to polyolefin mixture byweight. The resulting matrix comprises (or consists essentially of)UHMWPE and HD polyethylene and the particulate filler distributedthroughout the matrix. This microporous material has a machine direction(MD) tensile strength of greater than 25 N/mm².

A process for improving the wet out time of an uncoated microporousmembrane was developed comprising the steps of: providing an ultrahighmolecular weight polyethylene (UHMWPE); providing a particulate silicafiller; providing a processing plasticizer where said processingplasticizer may be a liquid at room temperature. Then mixing UHMWPE,filler and processing plasticizer together to form a mixture, having aweight ratio of filler to UHMWPE of from 1:9 to 15:1 by weight. Themixture is then extruded to form a sheet. The sheet is then processed,where processing is selected from the group consisting of: calendering,casting or blowing. The processed sheet then undergoes an extractionstep where all or part of the processing plasticizer is extracted fromthe sheet to produce a microporous matrix sheet which comprises UHMWPEand the particulate filler. In this matrix the filler is distributedthroughout the matrix. The microporous matrix sheet is then calenderedto produce a microporous membrane with a reduction in thickness of atleast 5%. The resulting microporous membrane typically exhibits areduction in wet out time of 50% or more over said microporous matrixsheet without the use of any chemical surface coating treatments.

Additionally a process for improving the wet out time of an uncoatedmicroporous membrane comprising the steps of: providing an ultrahighmolecular weight polyethylene (UHMWPE); providing a particulate silicafiller; providing a processing plasticizer where said processingplasticizer may be a liquid at room temperature. Then mixing UHMWPE,filler and processing plasticizer together to form a mixture, having aweight ratio of filler to UHMWPE of from 1:9 to 15:1 by weight. Themixture is then extruded to form a sheet. The sheet is then processed,where processing is selected from the group consisting of: calendering,casting or blowing. The processed sheet then undergoes an extractionstep where all or part of the processing plasticizer is extracted fromthe sheet to produce a microporous matrix sheet which comprises UHMWPEand the particulate filler. In this matrix the filler is distributedthroughout the matrix. The microporous matrix sheet is then stretched inat least one stretching direction to a stretch ratio of at least about1.5 to produce a stretched microporous matrix sheet. This stretchedmicroporous matrix sheet is then calendered to produce a microporousmembrane with a reduction in thickness of at least 5%. Where theresulting microporous membrane, typically exhibits a reduction in wetout time of 50% or more over the microporous matrix sheet without theuse of any chemical surface coating treatments.

Test Procedures

Thickness—The membrane thickness values are reported in units ofmicrometers (μm) and were measured using ASTM D374.Puncture Strength—The units of puncture strength are newtons and thetest procedure was ASTM D3763.Tensile Strength—Tensile strength was measured using ASTM D882 and theunits are N/mm2.Electrical Resistance—The units of electrical resistance are mohm-cm².Shrink Testing—Both MD and TD shrink values were measured using amodified version of ASTM D4802. The samples were cut into 5 inch (12.7cm) squares and put into an oven for 10 minutes at 100° C. The units arepercentage of change from the original dimension.Basis Weight—Basis weight was determined using ASTM D3776 and the unitsare grams per square meter.Hg porosity—This was measured using Hg intrusion porosimetry.Gurley—The units are sec/10 cc and were measured by TAPPI T536 method.Wetout Time—A visual technique whereas a sample is gently placed (notimmersed) on the surface of water, and the time (in seconds) it takesfor the membrane to begin to darken is called the wetout time.Equipment—Calendering rolls used in these tests were stack rolls havinga diameter of 8 inches or 20.3 centimeters.

As can be seen from the Examples which follow, the resulting stretchedthen calendered microporous material exhibits improved dimensionalstability properties over a membrane which has only been stretched.

EXAMPLES

Example A is membrane containing the following:

Ratio Polymer Filler Filler- Example A UHMWPE SiO2 Plasticizer MinorsPolymer Extrusion 9.6% 25.0% 64.0% 1.4% 2.6 Extraction 23.5% 61.1% 12.0%1.4% 2.6

Now taking the material from Example A additional samples were preparedusing tenter frame equipment. This equipment allows for both uniaxialand biaxial stretching. The following parameters were used to producethese samples:

TABLE 1 Stretched Membrane Characteristics Modulus- Tensile- Net BackwebPuncture MD MD Sample # Stretch % (μm) (N) (MPa) (N/mm²) ElongationMD %A-10 300 173 6.7 71.2 11.9 23 A-11 300 173 8.3 69.6 14.1 27 A-12 400 1479.9 170.8 29.9 21 A-13 400 144 7.9 96.1 18.5 22 A-14 500 124 7.4 261.134.3 17 A-15 500 120 7.3 146.3 24.0 19 A-16 300 159 9.9 101.8 23.3 40A-17 400 150 11.4 149.5 31.3 28 A-18 300 × 350 80 3.3 23.5 4.6 21 A-19200 × 350 106 5.7 27.3 11.2 54A-18 and A-19 samples were biaxially stretched and produced using asequential stretching device. The other samples refer to stretchedmembranes in the MD direction (uniaxial) only.

TABLE 2 Stretched Membrane Characteristics (Continued) Modulus- Tensile-TD TD Elongation- Shrinkage- Shrinkage- Basis wt Gurley Sample # (MPa)(N/mm²) TD % MD % TD % (gsm) (sec/100 cc) A-10 10.6 3.7 204 −3.9 <1 59.558.8 A-11 8.6 3.9 229 −3.9 <1 58.7 56.0 A-12 7.1 3.7 303 −11 <1 45.8119.6 A-13 8.8 3.4 205 −3 <1 47.5 59.4 A-14 6.3 2.8 244 −7 <1 38.3 90.2A-15 7.4 3.2 219 −2.3 <1 41.7 53.4 A-16 11.6 3.9 234 −10.7 −0.2 55.896.3 A-17 8.7 3.4 230 −12.3 −0.3 47.6 86.7 A-18 21.3 6.2 35 −32 −44 15.615.4 A-19 19.6 8.3 54 −37 −44 20.5 36.8

TABLE 3 Stretched/Compressed Membrane Conditions and CharacteristicsCalender Tensile Tensile Gap Calender Temp Thickness MD TD Sample # μmPressure ° C. μm Puncture N N/mm2 N/mm2 A-16-F 0 Full 110 53.3 9.1 72.912.1 A-17-F 0 Full 110 48.3 10.4 86.0 11.5 A-16-M 25 Moderate 110 76.29.6 52.6 8.8 A-17-M 25 Moderate 110 71.1 10.5 77.4 10.5 A-16-S 100Slight 110 149.9 10.1 26.9 4.3 A-17-S 100 Slight 110 142.2 10.8 31.4 3.7A-16-F 0 Full 135 55.9 10.5 74.8 14.2 A-17-F 0 Full 135 53.3 11.1 90.114.2 A-16-M 25 Moderate 135 86.4 10.1 26.3 5.4 A-17-M 25 Moderate 13578.7 10.9 39.8 5.8 A-16-S 100 Slight 135 157.5 9.6 24.7 4.2 A-17-S 100Slight 135 149.9 10.8 28.3 4.2 A-18-F 0 Full 121 17.8 4.3 41.6 42.0A-18-M 20 Moderate 121 22.9 3.3 28.5 28.2 A-19-F 0 Full 121 20.3 8.264.9 54.9 A-19-M 20 Moderate 121 30.5 7.0 47.6 34.0

TABLE 4 Stretched/Compressed Membrane Characteristics Elonga- Elonga-Shrink- Shrink- Wetout tion - MD tion - TD age - MD age - TD Time Sample# % % % % sec A-16-F 47 195 −0.5 0.9 18.0 A-17-F 34 193 −0.5 1.0 18.0A-16-M 52 222 −2.6 0.1 41.0 A-17-M 39 244 −1.4 0.3 42.0 A-16-S 46 208−6.5 −0.2 115.0 A-17-S 31 242 −7.0 −0.3 160.0 A-16-F 51 188 −0.1 0.920.5 A-17-F 36 221 −0.4 0.8 18.5 A-16-M 46 207 −0.9 0.1 52.0 A-17-M 36235 −1.3 −0.1 46.5 A-16-S 56 208 −6.5 −0.2 79.5 A-17-S 39 261 −7.0 −0.341.0 A-18-F 26 35 −0.8 0.0 4.5 A-18-M 24 50 −3.2 −4.6 9.0 A-19-F 50 470.2 0.1 2.5 A-19-M 52 67 −2.4 −1.6 9.0Wetout times for uncalendered A-16, A-17, A-18 and A-19 were notobtained and found to be much greater than 10 minutes.

From the data presented in these Tables, several advantages can be seenwith the present process compared to the prior art. First, the stretchedand then calendered films have greatly improved dimensional stability,even at elevated temperatures. The thickness which can be achieved bythe stretching process alone is limited and thinner membranes can beachieved by calendering the membrane after stretching. Physical strengthis much improved after the calendering of a stretched microporousmaterial. Finally, the calendering process reduces the pore size andvarious degrees of calendering can be used to adjust to the desired poresize.

The present invention may be embodied in other forms without departingfrom the spirit and the essential attributes thereof, and, accordingly,reference should be made to the appended claims, rather than to theforegoing specification, as indicated the scope of the invention.

1. A method for producing an ultracapacitor comprising the steps of:providing a negative porous electrode in contact with a negativeconducting plate; providing a positive porous electrode in contact witha positive conducting plate; providing an ultracapacitor separatorseparating said negative porous electrode from said positive porouselectrode; providing an electrolytic solution; said electrolyticsolution impregnating said negative porous electrode, said positiveporous electrode, and said ultracapacitor separator; and curing saidultracapacitor at a temperature of at least 200° C.
 2. The method ofmanufacturing an ultracapacitor of claim 1 where said ultracapacitorseparator having a change in thickness of less than 8% at a curingtemperature of at least 200° C.
 3. The method of manufacturing anultracapacitor of claim 1 where said ultracapacitor separator having asurface resistance of less than 30 ohms/cm² at any temperature less than200° C.
 4. The method of manufacturing an ultracapacitor of claim 1where said ultracapacitor separator including a microporous materialcomprising: an ultrahigh molecular weight polyethylene (UHMWPE) and aparticulate filler distributed throughout said microporous material;where said filler constitutes from about 5 percent to 95 percent byweight of said microporous material; where said microporous material hasa network of interconnecting pores communicating throughout saidmicroporous material, said pores constituting at least 25 percent byvolume of said microporous material, these pores create a poredistribution; where said microporous material has no pores greater insize than 1.0 micrometers; and where change in volume divided by log dfor the pores of this microporous material is less than 2 cc/g for theentire pore distribution.
 5. The method of manufacturing anultracapacitor of claim 4, where said microporous material has a machinedirection (MD) tensile strength of greater than 25 N/mm².
 6. The methodof manufacturing an ultracapacitor of claim 4, where said filler isselected from the group consisting essentially of: silica, precipitatedsilica, silica gel, fumed silica, mica, montmorillonite, kaolinite,asbestos, talc, diatomaceous earth, vermiculite, natural and syntheticzeolites, cement, calcium silicate, clay, aluminum silicate, sodiumaluminum silicate, aluminum polysilicate, alumina silica gels, glassparticles, carbon black, activated carbon, carbon fibers, charcoal,graphite, titanium dioxide, lead oxide, tungsten, iron oxide, copperoxide, zinc oxide, antimony oxide, zirconia, magnesia, alumina,molybdenum disulfide, zinc sulfide, barium sulfate, strontium sulfate,calcium carbonate, and magnesium carbonate.
 7. The method ofmanufacturing an ultracapacitor of claim 4 where said UHMWPE is mixedwith a high density (HD) polyethylene to produce a polyolefin mixture;where said polyolefin mixture has at least 50% UHMWPE by weight of saidpolyolefin mixture; and where said filler to said polyolefin mixture isin a range of from 1:9 to 15:1 filler to polyolefin mixture by weightand where said matrix comprises UHMWPE and HD polyethylene and saidparticulate filler distributed throughout said matrix.
 8. The method ofmanufacturing an ultracapacitor of claim 4 where said microporousmaterial being made from a precursor material where said microporousmaterial has a reduction of thickness of 5% or more from said precursormaterial.
 9. An ultracapacitor produced by the method of claim
 1. 10. Anultracapacitor produced by the method of claim
 2. 11. An ultracapacitorproduced by the method of claim
 3. 12. An ultracapacitor produced by themethod of claim
 4. 13. An ultracapacitor produced by the method of claim7.
 14. An ultracapacitor produced by the method of claim 8.